1. Field of the Invention
The invention relates to a method and a device for motion estimation, and to a video display apparatus comprising a motion-compensated interpolation device.
2. Description of the Related Art
Motion vectors are used in a range of applications, such as coding, noise reduction, and scan rate conversion. Some of these applications, particularly the frame rate conversion, require the true-motion of objects to be estimated [10,11]. Other applications, e.g., interlaced-to-sequential scan conversion, demand a high accuracy of the motion vectors to achieve a low amplitude of remaining alias [12,13]. Finally, there is a category of applications, e.g., consumer applications of motion estimation, where the cost of the motion estimator is of crucial importance [14,15]. Several algorithms have been proposed to achieve true-motion estimation [3,10,11,15-17]. Algorithms have also been proposed to realize motion estimation at a low complexity level, e.g., [3,14,15,18-20], and in addition to the pel-recursive algorithms that usually allow sub-pixel accuracy, see e.g., [21,22], a number of block-matching algorithms have been reported that yield highly accurate motion vectors [10,23,24].
Some years ago, a recursive search block-matcher was proposed which combines true-motion estimation as required for frame rate conversion with the low complexity constraint necessary for consumer applications [3]. This design has been commercialized in a Philips IC (MELZONIC, SAA4991) [6,25] which applies motion estimation and compensation techniques to improve the motion portrayal of film material when shown on television, and to eliminate the blurring of image detail in the case of motion as it occurs when displaying sequences at a picture refresh rate differing from the transmission rate. The most challenging task of such processing is the estimation of motion vectors indicating whether, at a given location of the screen, objects are moving or not, and if so, how fast and into which direction. In the known IC, this task is performed by a so-called block-matcher which divides the image into blocks and calculates a motion vector for every block of pixels by minimizing a match criterion. The risk of such processing is that the motion-compensated image, interpolated from neighboring images and using the motion vectors, may show block distortions if the motion vector field suffers from unwanted inhomogeneities. To reduce this risk to an acceptable level, the IC in [6] applies a block-matcher with improved consistency based on spatial and temporal prediction of candidate vectors [3]. An advantageous side effect of this approach to motion estimation is the very significant reduction of processing power required for the function, which is particularly due to the very limited candidate vector count.
The article xe2x80x9cLayered representation for motion analysisxe2x80x9d by J. Y. A. Wang and E. H. Adelson, in the Proceedings of the 1993 IEEE Computer Society conference on Computer vision and pattern recognition, pp. 361-366, [29] discloses a set of techniques for segmenting images into coherently moving regions, using affine motion analysis and clustering techniques. An image is decomposed into a set of layers along with information about occlusion and depth ordering. A scene is analyzed into four layers, and then a sequence is represented with a single image of each layer, along with associated motion parameters.
It is, inter alia, an object of the invention to provide a motion estimator having a further reduced complexity. To this end, a first aspect of the invention provides a method and a device for estimating motion in video data. A second aspect of the invention provides a method and a device for motion-compensating video. A third aspect of the invention provides a video display apparatus including said device for motion-compensating video data.
In a method of estimating motion in accordance with a primary aspect of the present invention, at least two motion parameter sets are generated from input video data, a motion parameter set being a set of parameters describing motion in an image, by means of the motion parameter set, motion vectors can be calculated. One motion parameter set indicates a zero velocity for all image parts in an image, and each motion parameter set has corresponding local match errors, such as, match errors determined per block of pixels. Output motion data are determined from the input video data in dependence on the at least two motion parameter sets, wherein the importance of each motion parameter set (determined by weighting factors W, see equations 17, 18 and between equations 20, 21) in calculating the output motion data depends on the motion parameter sets"" local match errors. Local match errors are to be understood in contrast with global match errors, such as, match errors calculated for the entire image.
In a method of motion-compensating video data in accordance with another aspect of the present invention, at least two motion parameter sets are generated from input video data, one motion parameter set indicating a zero velocity, and each motion parameter set having corresponding match errors, and output video data are interpolated from the input video data in dependence on the at least two motion parameter sets, wherein the importance of each motion parameter set in calculating the output video data depends on the motion parameter sets"" match errors.
In one embodiment, the reduction is so significant that the processing can run on a fully programmable device, more particularly, the Philips TriMedia processor.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.